Coating magnesium



Patented Jan. 5, 1937 UNITED STATES PATENT OFFICE COATING MAGNESIUM Herman I. Lodeesen, Detroit, Mich., asslgnor, by

mesne assignments, to The Patents Corporation, Detroit, Mich, a corporation of Michigan No Drawing. Application December 22, 1934,

Serial No. 158.825 7 by the use of oxalic acid, and this invention re- 7 lates to the proper use of oxalic acid for producing the best results.

A coating on magnesium can be formed by emlb ploying a solution of oxalic acid at various temperatures and containing various materials in addition to the oxalic acid. Also magnesium can be coated by a number of other organic acids, but so far as found, the best coating can be pro- 0 duced by a somewhat dilute solution consisting essentially of oxalic acid and. employed at approximately boiling temperature.

A 1% solution of oxalic acid at boiling tempera ture saturated with magnesium produces a very satisfactory coating on magnesium and magnesium alloys in from two to ten minutes, depending upon the nature of the surface and the alloy. The saturation of the solution may be obtained merely by boiling magnesium articles therein, if so desired, in which case the first articles are pickled for a considerable length of time and the final coatings on these first articles are not as good as subsequent coatings. It is preferable to supply a compound of magnesium or some other compound for starting purposes. A small'amount of magnesium carbonate, such as /2 gram to 100 cc. water is sufllcient to form a good coating solution, or an equivalent amount of magnesium oxide may be used, or other magnesium com- 4% pound.

It has been found also that inemploying a freshsolution, a small amount of a compound containing substantially any metal below magnesium in the electromotive series will take the place of the magneisum compound for effecting a prompt coating action. Among the compounds which have been employed eifectively for this purpose are compounds. of. iron, zinc, cadmium, cobalt, copper, silver, molybdenum, manganese and aluminum. As little as one-tenth per cent of aluminum sulphate is generally effective for making the solution coat promptly. After the solution has been used to coat a few panels, the work is satisfactory regardless of whether or not any compound of any metal has been added and where a compound such as aluminum sulphate, or any other compound of the metals mentioned is employed for purposes of obtaining a coating when starting a new solution,- there is no need of adding any more oil this compound when 5 replenishing the solution, since as satisfactory a coating for most purposes is obtained without any such addition.

' There are a number of the metals mentioned which change the appearance of the coating to a 10 trade as sparkle, in connection with the phosphate coatings, but this may be avoided by using small amounts of the iron and at proper temperatures.

As previously indicated, coatings may be obtained at lower temperatures, and even at room 25 temperature a coating furnishing some advantages may be obtained, particularly with the use of some compounds other than magnesium,

' the use of ferric salts being particularly good for this purpose. However these coatings are not as a satisfactory as the coating resulting from the use of oxalic acid at approximately boiling temperatures, which produces a thin flne grained coating so adherent that it is a substantially integral portion of the coated article and does not flake off when the article is bent. It greatly increases the resistance of the article to corrosion and forms a, particularly good base for paint. It has been found by tests to form a materially better base for paint than the phosphate coatings which have i been produced hitherto.

While all the dicarboxylic and hydroxydicarboxylic acids of the fatty acid series and the carboxylic acids having but one carbowl group and the sulphonic acids of the aromatic series and at even some additional acids, such as glycolic and citric of the fatty acid series and some other acids of the aromatic series, have a coating eflect upon magnesium when properly employed, none of these is as satisfactory as the coating produced by 5b oxalic acid employed in the manner mentioned above. The nearest equivalents of oxalic acid are, as should be expected, those most closely related thereto, that is, the other dicarboxylic acids of the fatty acid series. Succinic, glutarlc and adlpic 5c acids have been used with good results and might be employed ii oxalic acid were not available, but these other acids are higher in price than oxalic acid and are somewhat interior in results.

While coatings may be produced by weaker solutions, and stronger solutions than 1% oxalic acid, the weaker solutions require a longer time and the stronger solutions have a tendency to pickle the work to a greater extent than the 1% solution, and, therefore, approximately 1% solution is the preferable concentration. This forms,

a,oee,a4:'z t

on a suriace the major ingredient in which 15'.

magnesium, a substantially integral, thin, adherent coating of masnesium oxalate.

What I claim is:-

A method of coating a surface the major ingredient of which is magnesium, which consists in treating said surface with an approximately 1% solution of oxalic acid at approximately boiling temperature.

- HERMAN J. LODEESEN. 

